Tungsten-halogen lamp

ABSTRACT

A tungsten-halogen lamp having an aluminosilicate glass envelope with a wedge base. Lead-in wires of molybdenum are secured through the base in a pinch seal and support an unstabilized tungsten coil filament by clamping. The lamp may include a getter in the form of a tantalum wire or strip which is also secured in the base pinch seal.

United States Patent 191 Westlund, Jr. et al.

TUNGSTEN-HALOGEN LAMP Inventors: Arnold E. Westlund, Jr.,

Manchester; Lewis H. Palmer, III, Marblehead; Emery G. Audesse, Salem, all of Mass; Leroy S. Huston, Derry, NH.

GTE Sylvania Incorporated, Danvers, Mass.

Filed: July 13, 1973 Appl. No.: 378,975

Assignee:

US. Cl 313/174, 313/222, 313/318 Int. Cl. H01k 1/38, l-lOlk l/44 Field of Search 313/318, 221-222,

References Cited UNITED STATES PATENTS 9/1965 Freeman 313/222 X 2/1970 Dum Baugh, Jr 313/221 11/1970 Van Der Linden et al..... 313/222 X OTHER PUBLICATIONS Coaten, I. R. Modern Tungsten-Halogen-Lamp Technology" Free. IEE, Power, Vol. 117, 10-1970, pp. 1953-1959.

Primary Examiner-James W. Lawrence Assistant Examiner-Wm. H. Punter Attorney, Agent, or FirmEdward J. Coleman 57] ABSTRACT A tungsten-halogen lamp having an aluminosilicate glass envelope with a wedge base. Lead-in wires of molybdenum are secured through the base in a pinch seal and support an unstabilized tungsten coil filament by clamping. The lamp may include a getter in the form of a tantalum wire or strip which is also secured in the base pinch seal.

10 Claims, 5 Drawing Figures TUNGSTEN-HALOGEN LAMP BACKGROUND OF THE INVENTION This invention relates to incandescent electric lamps of the tungsten-halogen type.

In such lamps, the tungsten, which is normally evaporated from the filament during operation, combines with the halogen to form a gaseous halide and is thus kept from depositing on the wall of the lamp envelope. The halide normally has a regenerating action, being used over and over again, because when it returns to the hot filament or lead-in wires, the halide will decompose, depositing the tungsten on the filament or lead-in wires. This halogen cycle is well known, and lamps utilizing it have been on the market.

Such lamps have previously been made in quartz tubes or bulbs, because of the high temperature which was considered necessary for operation. The internal filament support rods in such lamps were tungsten and, due to the low thermal expansion of the quartz, molybdenum ribbons had to be used in the seal. A tungsten rod was welded to one end of each ribbon, while an external lead wire was welded to the other end. Typically the filament was supported in the tungsten rods or leads by an overwind, i.e., slipping the coiled end leads of the filament over the supporting leads. Accordingly, the coil is stabilized to set the coil configuration and spacing. Such a lamp construction is relatively expensive from the standpoint of both materials and manufacturing costs.

In order to reduce this expense, US. Pat. No. 3,641,386 describes a tungsten-halogen lamp construction which permits the use of less costly borosilicate glass for the envelope material. This permits tungsten lead-in wires to be sealed directly through the glass. In order to operate at temperatures satisfactory for the borosilicate glass, however, the bulb diameter is made much greater than that used with a quartz-halogen lamp. Further, the end of the bulb is sealed to a long flare, or reentrant stem, and a ceramic disc is provided to thermally shield the press from the filament radiation.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a small high intensity lamp at moderate cost.

It is a particular object of the invention to provide a tungsten-halogen lamp of significantly reduced size and expense and which is particularly suitable for manufacture by high speed automatic assembly methods.

A further object is to provide a tungsten-halogen lamp of improved performance and which is particularly suitable. for miniature lamp applications.

These and other objects, advantages and features are attained, in accordance with the principles of this invention, by a wedge-based tungsten-halogen lamp having an aluminosilicate glass envelope with molybdenum wire leads passing through a pinch seal thereof and supporting an unstabilized tungsten filament by clamping at each end. In one embodiment, a tantalum wire is supported from the pinch seal to provide getter- BRIEF DESCRIPTION OF THE DRAWINGS This invention will be more fully described hereinafter in conjunction with the accompanying drawings, in which:

FIG. 1 is a front elevational view plartly in section of one embodiment of a tungsten-halogen lamp according to the invention;

FIG. 2 is a side view of the lamp of FIG. 1;

FIG. 3 is a fragmentary perspective view of the base or terminal end of the lamp on a greatly enlarged scale;

FIG. 4 is a front elevational view partly in section of a lamp containing a tantalum wire getter according to the invention; and

FIG. 5 is a front elevational view partly in section of a lamp containing a tantalum strip getter according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, a first embodiment of a tungsten-halogen lamp according to the invention is shown comprising an hermetically sealed lamp envelope 2 of hard glass tubing having a flat pinch seal 4 defining one end thereof and an exhaust tip 6 defining the other end thereof. The lamp is filled with an inert gas, such as argon, nitrogen, krypton, or a mixture thereof, and a halogen additive such as bromine, for example, in the form of hydrogen bromide. The total pressure of the admixed halogen and inert fill gas may range from 2 to 7 atmospheres, at room temperature, depending upon the fill gas composition and the voltage, lumen and life ratings for which the lamp is designed.

A tungsten filament 8, typically of either a C6 or CC6 coil configuration, is supported within the lamp envelope by a pair of molybdenum lead-in wires 10 extending through and sealed into the flat pinch 4. The filament spans the inner ends of the lead-in wires, with the ends of the coiled tungsten being clamped by the molybdenum lead-in wires at 14 and 16, respectively. Such a clamp type filament-mount is permitted by the ductility of the molybdenum lead-in wires and is particularly suitable for high speed machine assembly.

A hard glass that has been found particularly suitable for use as envelope 2 is aluminosilicate, such as Corning 1,720 glass. This material operates reliably at temperatures up to 500C, yet ismuch less expensive than quartz. Further, at the room temperature setting point, aluminosilicate glass has a coefficient of thermal expansion of about 52 X 10 in./in./C, while the thermal expansion of the molybdenum wire is about 55 X 10 7 in./in./C. Accordingly, this envelope material permits a simple match seal to be used in securing the lead-in wires 10 through the flat pinch 4, and obviates the need for an intermediate molybdenum ribbon connection as employed in quartz seals. During sealing the lamp is flushed with an inert gas, such as argon or nitrogen, so as to control the amount of oxide formed in the molybdenum leads. Preferably, the oxide extends into the seal region to about one-third of the length thereof to provide a good seal. An unexpected advantage of this through-wire configuration is a reduction in the power loss through the seal. For example, in a 69 watt, 14 volt aluminosilicate lamp having 0.0l3 inch molybdenum lead-in wires, the voltage loss in the seal was measured as 1.95 watts, while the loss in a similar quartz lamp having molybdenum ribbons interconnected in the seal was 2.65 watts.

Aluminosilicate glass has also been found to be advantageous over borosilicate for tungsten-halogen lamp 3 applications. The aluminosilicate lamp remains clean with relatively light halogen concentrations, to thereby provide a longer operating life. Borosilicate lamps appeared .to require a relatively large halogen concentration to remain clean, but this results in a prohibitively short lamp life.

Consistent with the objects of miniaturization and reduced cost, a wedge base lamp configuration is provided by bending and folding the externally protruding molybdenum leads to serve as contact terminals, and providing transverse indents underlying these terminals in the pinch seal area. With this configuration, the lamp may be used in a conventional automotive type lamp mount by a straight push-in movement of the lamp into the socket in the direction of the lamp axis, the indents providing the desired detent action with the twin set of double prong spring terminals typically employed in such sockets.

More specifically, lead-in wires have terminal portions which protrude endwise from the outer end of flat pinch 4 and serve as the terminal contacts of the lamp. Outwardly of the fiat pinch 4, the terminal portions 20 of the lead-in wires are retroverted or bent back upon themselves as indicated at 22 to form double-legged open loop-shaped contact members 24. The free ends 26 of the retroverted terminal portions of the lead-in wires are reentered and embedded within the flat pinch 4, as shown in FIG. 3, to thereby further anchor the wire loop contacts in place and rigidly support them from the pinch seal against distortion, as when engaged with the contacts of a lamp socket. To permit the making of the electrical contact to the lamp at the side of the flat pinch, as well as at the outer ends thereof, the wire loop contact members 24 are bent around the end of the pinch seal preferably around the opposite flat sides thereof, to provide side contact portions 28 extending approximately parallel to and alongside the opposite flat sides of the pinch seal 4 and terminating past an underlying transverse indent 18 therein. The indent 18 does not traverse the entire width of the pinch seal but extends from the edge of one of the flat sides of the pinch a sufficient distance to underlie a respective one of the loop contacts 24. Hence, two indents 18 are provided on each side of the flat pinch as illustrated.

In many applications, it may also be desirable to getter the hydrogen and oxygen contamination diffused from the glass envelope 2. A particularly useful means for gettering a tungsten halogen lamp is described in a copending application Ser. No. (D-7290-L), assigned to the present assignee, wherein a piece of tantalum is strategically employed in the lamp. Specifically, it has been determined that tantalum will getter oxygen and hydrogen in appreciable amounts if its temperature is above 300C. The optimum temperature is 350C but gettering action is satisfactory between 300C and 450C, while the getter action on bromine or nitrogen is negligible in this range. As the temperature rises above 450C the gettering of bromine becomes appreciable. Consequently, the location ofthe tantalum getter within the tungsten-halogen lamp envelope is controlled such that the temperature of the tantalum is between about 300C and 450C, and sufficient tantalum is employed to getter all the oxygen and hydrogen available, as empirically determined.

FIGS. 4 and 5 illustrate two embodiments of this tantalum getter concept as applied to the lamp of FIG. 1.

In FIG. 4, a piece of tantalum wire 30 is anchored in the fiat pinch 4 and located so that the operating temperature of the getter portion of the wire extending into the envelope is between about 300C and 450C. For convenience in assembly, the tantalum wire initially may be welded to one of the molybdenum lead-in wires, and thereafter both the lead-in and tantalum wirepinchsealed in the same operation. This approach assures consistent location of the tantalum wire in the desired temperature region of the lamp, and anchoring a portion of the tantalum in the pinch seal 4 effects a degree of temperature control by assuring a heat sinking capability to the temperature of the seal region. FIG. 5 illustrates an alternative embodiment wherein the tantalum is inserted in the form of a strip welded to one of the lead-in wires.

Use of a tantalum getter as described above has been found to providea more favorable statistical failure distribution for long life lamps by removingmost of the impurities detrimental to the halogen regenerative cycle operation.

The described lamps are designed so that the maximum operating temperature on any part of the aluminosilicate envelope 2 is less than 500C. For example, in an embodiment of the lamp of FIG. 4 as a 50 watt, 14 volt, 200 hour lamp in a T3-% bulb: the outside diameter of envelope 2 is about 0.405 inch; the overall axial length is about 1.138 inch; the axial length of the flat pinch 4 is about 0.300 inch; and the filament is a CC6 tungsten coil supported about 0.700 inch from the lower edge of the lamp base by molybdenum lead-in wires of 0.012 inch diameter. The inert fill gas is argon, and the halogen is added in the form of hydrogen, bromide; total absolute fill pressure is about 5 atmospheres, with 0.97 percent thereof being attributable to the halogen. During operation, the maximum bulb wall temperature, measured near the filament, was about 475C. The filament coil temperature was about 3,200K, and the lamp was rated at 1,200 lumens output. The tantalum wire getter 30 extends about 0.120 inch into the lamp envelope below the filament and has a minimum temperature (near the seal) of about 300C and a maximum temperature (at the tip) of about 400C.

Although the invention has been described with respect to specific embodiments, it will be appreciated that modifications and changes may be made by those skilled in the art without departing from the true spirit and scope of the invention.

What we claim is:

l. A tungsten-halogen incandescent lamp comprismg:

a tubular aluminosilicate glass envelope having an exhaust tip sea] at one end and a flat pinch seal at the other end;

a fill of inert gas and halogen within said envelope;

a pair of molybdenum lead-in wires passing into said envelope and sealed through the flat pinch thereof;

a coiled tungsten filament supported within said envelope by said lead-in wires; and

said flat pinch of said envelope having transverse indents on both sides, and said lead-in wires having terminal portions extending outwardly from the end of said flat pinch, said terminal portion of each wire being retroverted and having its free end reentered and anchored within the free end ofsaid flat pinch, said terminal portion of each lead-in wire protruding from the fiat pinch being bent around the end of and alongside said fiat pinch and terminating past an underlying transverse indent therein, whereby a wedge base is provided on said lamp.

2. A lamp according to claim 1 wherein the maximum operating temperature on any part of said envelope is less than 500C.

3. A lamp according to claim 1 wherein said halogen is bromine.

4. A lamp according to claim 3 wherein said inert gas is selected from the group consisting of argon, nitrogen, krypton and mixtures thereof.

5. A lamp according to claim 4 further including a piece of tantalum wire anchored in said flat pinch and having a portion disposed as a getter within said envelope, said tantalum wire being so located that the operwires are clamped about each end of said tungsten filament.

8. A lamp according to claim 1 wherein said pinch seal has opposed flat sides, the retroverted terminal portions of said pair of lead-in wires form first and second loops, respectively, said first loop being bent around the end of said pinch seal and extending approximately parallel to one of the flat sides thereof, and said second loop being bent around the end of said pinch seal and extending approximately parallel to the other of the fiat sides thereof.

9. A lamp according to claim 1 further including a piece of tantalum anchored in said flat pinch and having a portion disposed as a getter within said envelope.

10. A lamp according to claim 9 wherein said halogen is present in the form of hydrogen bromide, said lead-in wires are clamped about each end of said tungsten filament, and said piece of tantalum is a wire having a length and location within said envelope selected so that the operating temperature of the getter portions of said wire is between about 300C and 450C. 

2. A lamp according to claim 1 wherein the maximum operating temperature on any part of said envelope is less than 500*C.
 3. A lamp according to claim 1 wherein said halogen is bromine.
 4. A lamp according to claim 3 wherein said inert gas is selected from the group consisting of argon, nitrogen, krypton and mixtures thereof.
 5. A lamp according to claim 4 further including a piece of tantalum wire anchored in said flat pinch and having a portion disposed as a getter within said envelope, said tantalum wire being so located that the operating temperature of said getter portion is between about 300*C and 450*C.
 6. A lamp according to claim 1 wherein the total pressure of said halogen and inert gas fill is within a range of from about 2 to 7 atmospheres at room temperature.
 7. A lamp according to claim 1 wherein said lead-in wires are clamped about each end of said tungsten filament.
 8. A lamp according to claim 1 wherein said pinch seal has opposed flat sides, the retroverted terminal portions of said paIr of lead-in wires form first and second loops, respectively, said first loop being bent around the end of said pinch seal and extending approximately parallel to one of the flat sides thereof, and said second loop being bent around the end of said pinch seal and extending approximately parallel to the other of the flat sides thereof.
 9. A lamp according to claim 1 further including a piece of tantalum anchored in said flat pinch and having a portion disposed as a getter within said envelope.
 10. A lamp according to claim 9 wherein said halogen is present in the form of hydrogen bromide, said lead-in wires are clamped about each end of said tungsten filament, and said piece of tantalum is a wire having a length and location within said envelope selected so that the operating temperature of the getter portions of said wire is between about 300*C and 450*C. 